The present invention relates to a television receiver for receiving television program signals which include stereophonic sound signals, and more particularly, to the generation of a psycho-acoustic stereophonic expansion effect with tonal compensation so that it acoustically appears to the listener that the spatial separation of the loudspeakers is greater than the actual physical separation.
Spatial stereo expansion in audio systems and television receivers is well known and has been available for many years. In such systems, the left and right channel signals are processed in a manner so that it appears to the listener that the distance of separation of the loudspeakers is greater than the actual physical separation of the loudspeakers. This is called psycho-acoustic expansion. Examples of spatial stereo expansion are shown in U.S. Pat. No. 5,208,493 of Lendaro et al., U.S. Pat. No. 4,831,652 of Anderson, both assigned to the present assignee, and U.S. Pat. No. 4,495,637 of Bruney. In such spatial expansion systems, a portion of an inverted signal from the other channel is added to the signal of the subject channel such that an ambience of spaciousness is introduced between the left and right channels. This feature has the desirable characteristic of making the acoustic perceived stereo image appear to be wider than the actual location of a pair of stereophonic loudspeakers. This is particularly desirable for a television receiver or small radio, where the spacing between loudspeakers is typically only about 26-80 cm. apart.
The most effective stereo expansion schemes boost the midrange frequencies of the difference signal because their half-wavelengths are approximately the same length as the distance between the ears of humans. Sounds that originate from the left or right of the listener produce phase cancellation between the two ears if they are of the appropriate (midrange) frequencies. This is one of the main direction-determining clues that we receive for the location of the origination of a sound.
Expanded stereo systems basically do the same thing, e.g., amplifying the difference of the L and R stereo channels (Lxe2x88x92R) relative to their sum signal (L+R). However, such expansion xe2x80x9cdrowns outxe2x80x9d vocals which typically are sum signals, and tends to make dialog less intelligible. Additionally, expansion systems amplify the mid frequency band of the difference signal relative to the low and high audio frequencies. This adds a midrange coloration to the sound.
A stereophonic expansion circuit for L and R signal channels, wherein each of the L and R signal channels have respective first and second amplifiers with each amplifier having respective non-inverting and inverting input terminals and an output terminal. A signal is coupled to a respective non-inverting input terminal and a first feedback path is coupled between the respective output terminal and the respective inverting input terminal. A filter couples the inverting input terminals together for providing a psycho-acoustic expansion effect. Tonal compensation for the expanded signals is provided by a passive frequency compensating circuit coupled between the input terminals and the output terminals.